From sci.math google group post: "How to generate random number sequences (in your head)"...<p>With the most relevant answer for you being George Marsaglia's:<p>~~~~~~~~~~~~~~~~<p>Choose a 2-digit number, say 23, your "seed".<p>Form a new 2-digit number:
the 10's digit plus 6 times the units digit.<p>The example sequence is
23 --> 20 --> 02 --> 12 --> 13 --> 19 --> 55 --> 35 --> ...<p>and its period is the order of the multiplier, 6, in the group of
residues relatively prime to the modulus, 10. (59 in this case).<p>The "random digits" are the units digits of the 2-digit numbers,
ie, 3,0,2,2,3,9,5,... the sequence mod 10.
The arithmetic is simple enough to carry out in your head.<p>This is an example of my "multiply-with-carry"
random number generator, and it seems to provide quite satisfactory
sequences mod 2^32 or 2^64 , particularly well suited to
the way that modern CPU's do integer arithmetic.<p>~~~~~~~~~~~~~~~~<p>source: <a href="https://groups.google.com/forum/?hl=en#!msg/sci.math/6BIYd0cafQo/Ucipn_5T_TMJ" rel="nofollow">https://groups.google.com/forum/?hl=en#!msg/sci.math/6BIYd0c...</a><p>edit: so with two people, one of you could chose the seed on alternate days based on some other criteria (like the N you already have or the things @nenadg mentioned (nearby people, cars, windows, cats, dogs, buildings, whatever you agree upon, those things are pretty pseudo-random))